Teacher:In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.
Teacher: Now, understand the problem? Solve this instance: Question: What year did construction begin on the dam that the river passes through before Afterbay Dam? Passage:The Bighorn River begins as the Wind River in the Rocky Mountains at Wind River Lake, near Two Ocean Mountain and the summit of Togwotee Pass. The Wind River flows southeast receiving the east fork of the Wind River from the north, and enters the Wind River Basin, flowing past Dubois and Johnstown, to Riverton, where it receives the Little Wind River. The river then changes direction to the northeast and then the north, flowing into Boysen Reservoir, which is formed by Boysen Dam. Below the dam it enters the Wind River Canyon, where the river narrows and forms many rapids. At the end of the canyon the Wind River widens out in an area called the Wedding of the Waters where it becomes the Bighorn River and enters the Bighorn Basin. The Bighorn continues northward, passing through Thermopolis, Worland, and Basin. At Greybull it receives the Greybull River, and about north of that confluence it enters Bighorn Lake, where it is joined by the Shoshone River. North of the confluence with the Shoshone, the reservoir narrows as the river enters the Bighorn Canyon, where it crosses into Montana. At the end of the canyon, the river passes through Yellowtail Dam and Afterbay Dam. The river turns to the northeast and enters the Great Plains. At Hardin the river is joined by the Little Bighorn River. Approximately downriver from the Little Bighorn, in Big Horn County, the Bighorn empties into the Yellowstone.
 Links: a. Bighorn Lake b. Boysen Dam c. Yellowtail Dam d. Bighorn Canyon National Recreation Area
Student:
c